Reduced Conductivity and Unique Electro-Magnetic Signature Zinc Alloy

ABSTRACT

An alloy, comprising up to 2% by weight of manganese and the balance zinc broadens the use of low cost zinc in coinage and token applications as well as in electrical and electronic applications. Additions of small amounts of manganese can have a significant effect on lowering the conductivity of zinc and its alloys.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit and priority of U.S. provisionalpatent application No. 61/870,485, filed on Aug. 27, 2013 and isincorporated herein by reference in its entirety.

BACKGROUND

Various metals are used in the coinage, electrical and electronicsmarkets with each metal having unique properties. Rolled and die castzinc products have been long standing product offerings in thesemarkets. The various base metal zinc alloys currently on the market havemeasured electrical conductivity values in the range of about 25% to 30%IACS based on the International Annealed Copper Standard (IACS) whichuses substantially pure copper as a 100% conductivity reference (100%IACS). These conventional zinc alloy electrical conductivity values,although providing certain unique electrical properties, have limitedzinc alloys from broader use in coinage, electrical and electronicsmarkets.

In the coinage market, the electrical conductivity and permeability ofthe metal provides a unique electromagnetic signature that is used forsecurity purposes. This electromagnetic signature provides an additionalsource of security in coin differentiation systems used in both thevending and banking industries. The more common metals and alloys usedin this industry, such as low carbon steels, stainless steels, nickel,copper, brasses, bronzes, cupronickel, aluminum bronze, and aluminum,have electrical conductivities either at or below 15% IACS or above 25%IACS.

There is a range from about 15% to 25% IACS in which a cost-effectivemetal or alloy could provide a unique range of electromagneticsignatures to provide additional security options for new or redesignedcoinage products. In addition, a more cost-effective zinc metal or alloyoption that can duplicate the electromagnetic signature of an existingcoinage product can provide a more economical solution to the coinagemarket while maintaining current coin differentiation parameters.

In the electrical and electronics market, the effective range ofelectrical conductivity of a material, along with other properties, canlimit its use. By expanding this effective range, the ease and/or costof production can be improved for existing uses and the range ofapplications for that material can also be expanded. Currently, rolledzinc alloys have been used in the automotive fuse market, as well as forshielding applications from electromagnetic and radio frequencyinterference and counterpoise grounding applications all utilizing thezinc alloys conventional electrical conductivity property range.Expanding the current effective electrical conductivity range for rolledzinc products would allow for additional uses in these existing marketsas well as expand the use of zinc alloys for additional applicationswithin this industry.

SUMMARY

Coins should inherently be lower in cost than their stated value toprevent destruction and manipulation of the coins for monetary gain.Zinc base alloys provide a low cost base metal from which to producecoinage which is less likely to be destroyed for its inherent materialvalue than more costly metals.

Coins can be identified as genuine by many methods including coin designfeatures, color, size, weight and shape, but are increasingly identifiedby their unique electromagnetic properties. This allows for quick andaccurate authentication by machines. These properties are inherentwithin the base metal or are an artifact of a combination of the basemetal and plated or coated surfaces, base metal and clad materials,and/or inclusion in a bi-metal coin system (two piece coin).

A range of new zinc alloys has been developed that has lower electricalconductivity than conventional zinc alloys thereby providing a wider andmore unique range of electromagnetic properties. This broadens currentsecurity options in coins.

A further advantage of this new range of conductivity of zinc alloys isa series of alloys with controllable conductivity for applications inelectrical and electronic markets. The alloy may be produced as a rolledproduct or in a traditional die casting process for variousapplications.

As noted above, current rolled zinc strip alloys and die cast zincmaterials have a limited conductivity range of about 25% to 30% IACS.This limits their use in both the coinage, electrical and electronicsmarkets. The alloys described herein expand the effective conductivityrange and electromagnetic signature of rolled and die cast zinc productsallowing for expansion of use in current markets and application intonew markets.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a graph depicting the effect on electrical conductivity of azinc based alloy by the addition of manganese to zinc;

FIG. 2 is a graph similar to FIG. 1 depicting the expanded effect onelectrical conductivity of a zinc based alloy by the addition ofmanganese and additional alloying agents;

FIG. 3 is a series of plots derived from a coin sorting machinedepicting the electromagnetic signatures of two zinc-manganese alloysformulated as described herein and compared with five other commoncoinage materials; and

FIG. 4 is a schematic perspective view of a blade fuse having a fusewire constructed with a zinc-manganese alloy.

DETAILED DESCRIPTION

A range of new zinc based alloys has been produced which containmanganese in the weight range of 0.01 to 2.0 percent for reducing theelectrical conductivity of zinc. These alloys show unique properties,most notably, an electrical conductivity lower than typical zinc andzinc alloys produced as strip. The initial alloys tested were simplebinary compositions of zinc and manganese and later, alloys containingother elements were tested. That is, alloys of zinc and manganese in theweight range noted above were combined with stabilizing agents, such ascopper in the amount of 0.1% to 1.2% by weight, aluminum in the amountof 0.001% to 0.60% by weight, titanium in the amount of 0.050% to 1.0%by weight, magnesium in the amount of 0.0001% to 0.050% by weight,cadmium in the amount 0.0001% to 0.50% by weight, chromium in the amountof 0.0001% to 0.50% by weight, iron in the amount of 0.0001% to 0.50% byweight and antimony in the amount of 0.0001% to 0.50% by weight.Stabilization refers to the ability of the zinc manganese alloy tomaintain a substantially constant IACS conductivity over time and overvarying temperature conditions. Any variation is referred to as “drift.”

For example, copper in the amount of about 0.1% to 1.2% by weight can beadded as a hardener to a zinc manganese alloy of 0.05% to 2% by weightmanganese, balance zinc. Titanium, magnesium, cadmium and chromium serveas grain refiners to produce smaller grains in the zinc manganese alloyand form intermetallic compounds which resist conductivity drift.

Titanium not only serves as a grain refiner in the zinc manganese alloy,it also lowers the IACS conductivity of the zinc alloy in its as caststate. Moreover, by adding titanium to the alloy, conductivity drift isreduced at any given level of manganese. A useful weight range oftitanium is 0.05% to 1% by weight of the alloy.

Testing has shown that the IACS test results places the conductivity ofthese new alloys in the range of 12% to 25% of IACS. Again, zinc alloysgenerally lie in the range of 25% to 30% of IACS. The conductivity ofthe alloys can be controlled with secondary effects based on rolling,heat treating and plating practice yielding processes for creating arange of electronic signatures within the zinc and manganese alloysystem. This range of conductivity is unique compared to generalcommercial alloys of common metals.

The ability to significantly adjust the conductivity of a zinc basedalloy with small amounts of manganese has many potential applications.This unique conductivity space of the alloy initially provides twopotential applications. The first is in the production of coinage with aunique electromagnetic signature (EMS). Coins for purposes of sorting orvending are often identified within a machine by a variety of criterion.The first is the physical parameters such as size and weight that areclearly evident and generally easy to copy. But the electro-magneticsignature of a coin consisting of a base metal that may or may not haveone or more plated layers, can be unique.

As described further below, the second application for this new range oflow conductivity alloys is within the electronics and fuse market, wherethe protective value of the fuse (amperage at the point of plannedfailure) is controlled by conductivity and geometry. Typically, a fuseis designed from a particular alloy and then the geometry is changed tocontrol the final fuse value. In some cases, it is desirable to make afuse for low amperage control, but which is complicated by the abilityto reliably produce small geometric cross-sections. An alloy of 50%lower conductivity would allow more manufacturability within the fuseindustry.

The key to this controlled conductivity is dominated by the quantity ofmanganese in the zinc, but the full range of potential alloys possiblemay need exploration to best control the space. Alloys with 0 to 2% byweight of manganese balance zinc, and preferably 0 to 1% by weight ofmanganese balance zinc have been found to produce conductivity in rangesnot previously achievable. The addition of copper to the zinc-manganesealloys acts as a hardener in the range of 0.1 to 1.2 weight percent.This addition increases the hardness without adverse affects onadjustment of conductivity by the manganese content in the zinc.Elements that fall in this grouping of increasing hardness and/orstrength of zinc-manganese alloys include copper, titanium, magnesium,aluminum, chromium, iron, antimony and/or cadmium. These elements alsoact as stabilizing agents to prevent IACS drift.

A cast alloy of zinc and manganese exhibits a certain initialconductivity. When rolled into a coil, the conductivity increases byabout 3% to 4% on the IACS scale. By adjusting the rolling process toroll at a lower metal temperature, the increase in conductivity can beminimized to about 1% to 2% IACS. Lower annealing temperature can alsohave an effect on lowering the conductivity of rolled alloys.

As shown in FIG. 1, the binary alloy of zinc and manganese in the rangeof 0.0 to 1.0% manganese produces a vast range of conductivities. Theaddition of manganese trends to lower conductivity. However, withvariation in processing conditions, such as rolling and platingpractice, a range of conductivities can be produced at varying manganeselevels. The lower boundary of the plot in FIG. 1 represents the as castalloy conductivity while the upper boundary of the plot represents thealloy conductivity after an aging process at about 220° F. producing adrift of about 5% IACS. Noticeable effects on the conductivity of zinccan be seen beginning around 0.01% by weight manganese and clearly at0.05% by weight manganese. These alloys contain from about 0.01% up to2% manganese, balance zinc, and more preferably 0.05% manganese up to 2%manganese balance zinc. More desirable effects on conductivity can beachieved with 0.05% to 1.0% by weight manganese, balance zinc. Ofcourse, additional stabilizing agents such as those noted above can beadded to any of these zinc-manganese alloys.

As noted above, the electrical conductivity of a zinc-manganese alloycan be further modified with the introduction of stabilizing agents intothe binary zinc-manganese alloys. As observed in FIG. 2, a larger rangeof conductivities can be produced with the addition of, for example, twoof the stabilizing agents noted above, thereby forming a quaternaryalloy with zinc and manganese. In this example, copper and titanium wereadded in the ranges noted herein to the zinc-manganese alloy asdescribed herein. Further expansion of the potential conductivity rangescan be achieved with varying the alloy processing conditions. The lowerboundary curve again represents the conductivity of the as-cast alloyand the upper boundary represents the conductivity of the alloy based onvarying process parameters and alloying agents.

The conductivity of a material is a strong driver in many parameters ofthe material's electromagnetic signature (EMS). Adjusting theconductivity of the base alloy for a through-alloy coin or plated coinwill impact the EMS of the coin and drive towards unique signals thatcan be used to differentiate a coin from other coins or slugs.

Blanks from two different representative zinc-manganese alloys wereproduced and coined using a common token die. These blanks were runthrough a coin sorting machine common to the industry (ScanCoin 4000)and the data compared to other common base or through alloy materialsused in coinage production, such as aluminum, bronze, cupronickel,stainless steel material and low carbon steel. The output data is shownin FIG. 3. Differences from other materials in only one of thesevariables or in the dimensions of the coin is all that is required toconsider a product unique. Differences in more than one characteristicstrengthens the security of the coinage product. These zinc-manganesebased alloys can create unique electromagnetic signatures as compared tomost commonly used metals used in the coinage market. The signalscircled in the plots in FIG. 3 highlight the different EMS signatureswhich can be used to differentiate coinage for security purposes.

As noted above, a second application for these lower conductivity alloysis within the electronics and fuse markets, where the protective valueof the component is often controlled by conductivity and geometry, suchas the amperage at the point of planned failure in a low-voltage bladefuse. An electronic component, such as a fuse, would be designed from aparticular alloy and then the geometry would be changed to control thefinal resistance or conductivity value required. In the case of a fuseused for low amperage control, the manufacturability is complicated bythe geometric cross-section required due to the inherent conductivity ofthe standard zinc alloys used.

A schematic example of a fuse 10 is shown in FIG. 4 wherein twoelectrical blade leads 12, 14 are connected by a thinner cross-sectionalarea element 18. Element 18 and/or the entire fuse 10 can be constructedfrom any of the zinc-manganese alloys described herein. Because of thehigher electrical resistance of the zinc-manganese alloys, the element18 can be increased in cross-sectional area to produce the sameresistance as a smaller conventional fuse element. Reducing conductivityof the fuse 10 and/or element 18 metal allows for an increase incross-sectional area of the element of a fuse to maintain an amperagerating which can aide in manufacturing. Increasing the cross-sectionalarea of the element can also result in increased reliability andconsistency of performance.

It will be appreciated by those skilled in the art that the abovereduced conductivity and unique electromagnetic signature zinc alloy ismerely representative of the many possible embodiments of the inventionand that the scope of the invention should not be limited thereto, butinstead should only be limited according to the following claims.

What is claimed is:
 1. An alloy, comprising: up to 2% by weight ofmanganese and the balance zinc.
 2. The alloy of claim 1, furthercomprising electrical conductivity in the range of 12 to 25% IACS. 3.The alloy of claim 1, wherein said manganese comprises 0.01% to 2% byweight of said alloy.
 4. The alloy of claim 1, further comprising copperin the range of 0.1% to 1.2% by weight.
 5. The alloy of claim 1, furthercomprising titanium.
 6. The alloy of claim 1, further comprising atleast one of the group consisting of copper, aluminum, magnesium,titanium, cadmium, chromium, iron and antimony.
 7. The alloy of claim 1,formed into a coin or token.
 8. The alloy of claim 1, formed into afuse.
 9. The alloy of claim 1, having an as-cast IACS conductivitymodified by a rolling process.
 10. The alloy of claim 1, furthercomprising a plating layer over said alloy.
 11. The alloy of claim 1,wherein said manganese comprises 0.05% to 1% of said alloy.
 12. Thealloy of claim 1, wherein said manganese comprises 0.01% to 1% of saidalloy.
 13. The alloy of claim 1, further comprising aluminum in theamount of 0.001% to 0.60% by weight.
 14. The alloy of claim 1, furthercomprising magnesium in the amount of 0.0001% to 0.50% by weight. 15.The alloy of claim 1, further comprising titanium in the amount of0.050% to 1.0% by weight.
 16. The alloy of claim 1, further comprisingchromium in the amount of 0.0001% to 0.50% by weight.
 17. The alloy ofclaim 1, further comprising iron in the amount of 0.0001% to 0.50% byweight.
 18. The alloy of claim 1, further comprising antimony in theamount of 0.0001% to 0.50% by weight.